(ABC News) -- A 6-year-old boy is in critical condition Monday at a Chicago hospital after he was trapped for more than three hours beneath a massive sand dune that collapsed on top of him at an Indiana park, a hospital spokeswoman told ABC News.
The boy, whose name has not been released, was walking with his parents along the sand dunes by Lake Michigan near Mount Baldy at Indiana Dunes National Lakeshore Park on Friday when a 124-foot sand dune swallowed him and took him under.
"[The boy's parents] didn't actually see the initial collapse," park ranger Bruce Rowe with the National Park Service told ABC News' Chicago station WLS-TV. "But when they got to him, they could actually see him for a little bit, tried to dig him out and that's when the total collapse, as they described it, happened."
Rescuers using heavy equipment worked to locate the boy buried deep beneath at least 11 feet of sand.
When they pulled him out from the sinkhole after three and a half hours of digging, he appeared to have vital signs, Laporte County Chief Deputy Coroner Mark Huffman told ABC News.
The boy, who is from Illinois, was taken to Franciscan St. Anthony Health in Michigan City, Ind., before he was airlifted to University of Chicago Children's Hospital, where he is currently recovering, Huffman said.
Huffman said the boy had ingested sand, and he will likely undergo extensive therapy to restore his lungs back to their former strength.
The boy may have been saved by an air pocket that was created by an old tree that was buried deep beneath the dune, Huffman said.
"We honestly don't know exactly what happened," Rowe told WLS-TV. "This is unprecedented. We've never had anything like this."
The area where the boy fell was off-limits to the public, Rowe said.
ABC News' Rachel Katz and Michael James contributed to this report. Click here for more from ABC News.